2015 DHI UK & Ireland Symposium
Modelling of Extreme Conditions for Wave Overtopping at Weymouth Bay
Oliver Way (Hyder Consulting), Tuesday 21 April 2015 at 16:00 - 16:20
A wave model study of Weymouth Bay was undertaken for Weymouth and Portland Borough Council to investigate flooding in the historical centre of Weymouth which is understood to be caused by tidal and fluvial waters overtopping flood defences, groundwater rising above ground level in response to high tides and heavy rain and wave overtopping along the open coast / Esplanade. The wave modelling results in this study are used to provide input conditions to the overtopping calculations which will in turn be used as inputs to the models of overland flow to provide flood extents. MIKE 21 SW was applied to simulate extreme wave conditions with combined extreme water levels. The model domain extends from Chesil Beach in the west to Lulworth Cove in the east. Extreme water level data were supplied by the Environment Agency for Weymouth from the Coastal flood boundary conditions for UK mainland and islands report (Environment Agency, 2012). Extreme wave values were also obtained from this Environment Agency report at offshore locations on the model boundary. Extreme wave conditions were considered for three directional sectors: south west, south and south east. A joint probability approach was applied for a range of return periods and climate change epochs. Wave data were extracted at nearshore locations along the beach front of Weymouth Bay. These data were used as input conditions for wave overtopping calculations (EurOtop) at site specific points along the beach to determine overtopping discharge rates along the beach front.